Accordingly, a conventional rolling door for fire protection may be exclusively classified, depending on braking mode, into two systems: one is fail-safe and the other is non-fail-safe. The rolling fire door is functioned as entrance guard for regular access, and then, based on its usage, there are advantages and disadvantages for the use of these two systems, respectively, as follows:
(1) Fail-safe mode: Brake is released immediately by a brake device to close the rolling fire door in the absence of electrical power no matter what reason therefore is. If the fire occurs in the presence of electrical power, the power is cut off by, for instance, smoke detectors, temperature sensors, and other fire detecting devices, or is mechanically cut off by fusible link devices which melt owing to high temperature in the fire in such a way that brake may be released and then the rolling door may be downwardly closed by its own weight. In this mode, the flame or escape of dense smoke may be blocked instantly when the fire occurs, if the cause for power failure is the fire indeed, whereby, a greater safety for fire prevention is the main merit. However, if the cause for this power failure is not the fire, inconvenience for users and influence on the regular access may take place, which is the main drawback in this mode.
(2) Non-fail-safe mode: The brake device is still presented in a brake-actuated state without closing the rolling fire door immediately in the absence of electrical power, no matter what reason therefor is. Only when the definite occurrence of fire is confirmed by, for instance, smoke detectors, temperature sensors, and other fire detecting devices, a current from a reserved power source, such as a capacitor, battery, and so on, is transiently supplied to the brake device for releasing the brake for a short period of time, or fusible link devices melt due to high temperature in the fire for mechanically operating the brake device to release the brake, in such a manner that the rolling fire door may be downwardly closed by its own weight. In this mode, the rolling fire door is not closed immediately in the absence of electrical power, also never resulting in confusing general users, provided that the fire is not the cause for power failure, which is the main merit. However, in case that the power failure is not induced by the fire, and in case that the fire point is further farther from the fire detecting devices or fusible link devices, it is impossible to close the rolling fire door instantly when the fire occurs. Therefore, the lack of safety for fire prevention is the main drawback in this mode.
FIG. 4 is a diagram redrawn according to U.S. Pat. No. 5,245,879, showing a typical fail-safe rolling fire door, as an example of conventional art. In this published prior patent document, there is disclosed a fire door having automatic reset in which a brake actuator may disengage the brake by the potential energy of a spring in the common condition. When electrified, the potential energy of spring may be overcome by a solenoid, moving the brake actuator and engaging the brake. When an abnormal power failure occurs, this brake actuator de-energizes the solenoid immediately, causing the brake actuator to disengage the brake under the effect of spring, in such a way that the rolling door may be downwardly closed by its own weight. Moreover, FIG. 5 shows a diagram of another fail-safe rolling fire door according to U.S. Pat. No. 5,850,865. In this published prior patent document, a brake is released automatically after the delayed time, such that the rolling door may be downwardly closed by its own weight, in an abnormal power failure condition.
In the above published patent document. The solenoid is used to operate a pair of drum brake shoes via a brake-operating pin. It will be appreciated by those skilled in the art that this mechanism is relatively complicated and thus the cost thereof is higher correspondingly. Moreover, this drum brake means must be regulated based on the degree of wear on the brake shoe, which is relatively troublesome in maintenance.